Cannot read property 'replace' of undefined BackboneJS - backbone.js

Question

I am trying to render a View(customerEditView) using modular BackboneJS but it gives me the uncaught type error.
this is my router.js file:
define([
'jquery',
'underscore',
'backbone',
'views/Customers/CustomerEditView',
'views/Customers/CustomerListView'
], function($, _, Backbone, CustomerEditView, CustomerListView) {
var Router = Backbone.Router.extend({
routes: {
"customers": "customerhome",
"editcustomer/:id": "editcustomer",
"newcustomer": "editcustomer",
},
customerhome: function () {
var customerListView = new CustomerListView();
customerListView.render();
},
editcustomer: function (id) {
var customerEditView = new CustomerEditView();
customerEditView.render({ id: id });
}
});
var initialize = function () {
var router = new Router;
Backbone.history.start();
};
return {
initialize: initialize
};
});
and this is my customerEditView file:
define([
'jquery',
'underscore',
'backbone',
'router',
'models/Customers/Customer',
'helper/Serialize',
'text!template/Customer/CustomerEditTemplate.html'
], function ($, _, Backbone, router, Customer, Router, serializeObject, CustomerEditTemplate) {
var CustomerEditView = Backbone.View.extend({
el: '.page',
events: {
'submit .edit-customer-form': 'saveCustomer',
'click .delete': 'deleteCustomer'
},
saveCustomer: function (ev) {
var customerDetails = $(ev.currentTarget).serializeObject();
var customer = new Customer();
customer.save(customerDetails, {
success: function (customer) {
Backbone.history.navigate('', { trigger: true });
}
});
return false;
},
deleteCustomer: function (ev) {
this.customer.destroy({
success: function () {
console.log('destroyed');
Backbone.history.navigate('', { trigger: true });
}
});
return false;
},
render: function (options) {
var that = this;
if (options.id) {
that.customer = new Customer({ id: options.id });
that.customer.fetch({
success: function (customer) {
var template = _.template(CustomerEditTemplate);
that.$el.html(template({ customer: customer }));
}
});
} else {
var template = _.template(CustomerEditTemplate);
that.$el.html(template({ customer: null }));
}
}
});
return CustomerEditView;
});